This invention relates to a high-voltage unit comprising at least a high-voltage electrode which carries a high voltage in the operating condition and a measuring divider/resistor arrangement which is connected between the high-voltage electrode and a measuring point wherefrom a measuring voltage corresponding to the variation in time of the high voltage can be derived.
Such a high-voltage unit in the form of a high-voltage generator for an X-ray generator is known from EP-OS 118 147. The measuring divider/resistor arrangement thereof forms a part of a high-voltage measuring divider which comprises a terminal resistor in addition to the measuring divider/resistor arrangement. A tapping of this high-voltage divider forms the measuring point and the voltage derived from this measuring point, amounting to a few volts, should be proportional as close as possible to the high voltage in a frequency range of from zero to some hundreds of kHz. The measuring divider/resistor arrangement is enclosed by a damping resistor connected to the high voltage. Comparatively high parasitic capacitances then occur. In order to prevent errors in the measuring voltage because of these parasitic capacitances, capacitors are connected parallel to the series-connected resistors constituting the measuring divider/resistor arrangement. These capacitors, which must be constructed so as to be able to withstand a part of the high voltage that depends on the number of resistors in the measuring resistor arrangement, are expensive and susceptible to high-voltage interference.
Furthermore, from DE-PS 37 14 945 there is known a capacitive-resistive voltage divider for measuring high voltages in intermediate-frequency and high-frequency X-ray generators, which divider comprises two mutually parallel high-voltage electrodes which are to be connected to the high voltage to be measured and wherebetween there is arranged a flat measuring electrode which extends parallel thereto. Between the measuring electrode and one of the high-voltage electrodes there is connected a measuring divider/resistor arrangement which consists of an inductance-free, meander-shaped resistor and which extends at an angle relative to the electrodes. When a voltage divider of this kind is built into a high-voltage generator, adequate clearance should exist between the external high-voltage electrodes and the grounded parts within the high-voltage generator, for example, the metal housing of the high-voltage generator, in order to prevent flash-overs. As a result, a comparatively large space is required for such an arrangement. Moreover, high electric field strengths occur at the edges of the high-voltage electrodes.